Rubber heel and sole, wear plug therefor, and method of manufacture



P 1941. A. AJESTERSON RUBBER HEEL AND SOLE, WEAR PLUG- THEREFOR, AND METHOD OF MANUFACTURE Filed Feb. 27, 1940 4 Sheets-Sheet 1 grwm'vfoz Jaw-a4 123367-301,

Sept. 23, 1941. A. A. ESTERSON 2,256,863 RUBBER HEEL AND SOLE, WEAR PLUG THEREFORLANID METBOD OF'MANUFACTURE ,F'iied Feb. 27, 1940 4 Sheets-Sheet 2 Fabric Drz'en Z] fllbertA Ester-sow,

Sept. 23, 1941. A. A. ESTERSON 2,256,863 RUBBER AND SOLE, WEAR PLUG THEREFOR, (AND METHOD OF MANUFACTURE I 4 Sheets-Sheet zs Filed Feb. 27, 1940 Q YVU W /i4, Zsierzsam ANUFACTURE Sept. 23, 1941. A. A. ESTERSON RUBBER HEEL AND SOLE, WEAR PLUG THEREFOR, AND METHOD OF M Filed Feb. 27, 1940- 4 Sheets-Sheet 4 Patented Sept. 23, 1941 FUNITED STATES PATENT oFricE RUBBER HEEL AND soLE, WEAR PLUG THEREFOR, AND METHOD or MANUFAC;

. TURE Albert A. Esterson, Baltimore, Md., assignor to Cats Paw Rubber Company, Inc., Baltimore, Md., a corporation of Maryland Application February 27, 1940, Serial No. 321,090

13 Claims.

This invention relates to rubber heels and soles for shoes, to certain constituent parts thereof, and to new and improved methods of manufacturing the same, including the manufacture of said parts and the final assembly of the parts corporated therein.

A further object of the invention resides in the provision of a new and improved non-skid and anti-slipping wear plug which is adapted to be incorporated in the heel or sole and which is so constructed as to offer a maximum of resistance to wear during the continuous and severe use to which articles of this character are ordinarily subjected.

It is a further object of the invention to provide in a rubber heel or sole, an improved nonskid or anti-slipping wear plug in which fabric cords are positioned accurately and permanently in perpendicular relation to the tread surface of the heel or sole, and in which the cords are integrally and-permanently bonded by-vulcanization to each other and to the rubber of the heel to provide an integral, unitary, non-laminated,

non-separable structure.

A. further object of the invention is to provide a method of constructing improved wear plugs and a novel method of incorporating the same in the heel or sole, so that the plugs are irremovably attached to the heel or sole so as to become, in effect, an integral part,thereof.

A still further object is to provide a rubber heel or sole inwhich the improved non-slipping wear plug is irremovably ailixed in such manner as to insure even d uniform wearing of the rubber heel or sole a d in such manner as not to detract from or impair the nature and desired resiliency of the heel and sole, of which the wear plug forms an integral part when in use.

It is a further object of the invention to provide a method of making non-slipping wear plugs, so that the same may be incorporated within and bonded by vulcanization to a rubber heel blank,

during a final moulding and vulcanizing step, without distorting the shape of the plugs or disturbing or changing the positions of the individual cord strands in the plugs. it is an object of the invention to provide wear To this end.

plugs which are inherently more resistant to distortion under heat and pressure in a mould than the rubber compound of the heel blank, whereby 'the plugs retain their shape in the final mould and the rubber compound of the heel blanks is forced to flow around the plugs and become bonded thereto, without distortion of the plugs.

With such objects in view, as well as other advantages which may be incident to the use of the improvements, the invention consists in the parts and combinations thereof and in the method steps hereinafter set forth and claimed, with the understanding that the several necessary elements constituting the same may be varied in explanation, have been made the subject of illustration.

In the drawings: Figure 1 is a bottom plan view of a rubber heel constructed in accordance with the present invention;

Figure 2 is a similar view of a rubber or com-' position half-sole;

Figure 3 is an enlarged vertical section on line 3-3 of Figure 1; I

Figure 4 is a diagrammatic plan view of an elongated sheet of cord fabric, uncoated, which is subsequently coated with an unvulcanized rubbr compound, cut into smaller blanks, and used in making the improved wear plug of the present invention;

Figure 5 is a fragmentary plan view of the cord fabric of Figure 4 on an enlarged scale;

Figure 6 is an 'eniargedjsectional view' on a plane parallelv to the warp cords, showing the fabric sheet with rubber compound calendered or otherwise applied to one face thereof;

Figure '7 is a similar viewgshowing rubber compound coatings on bothfaces thereof;

Figure 8 is a diagrammatic side elevation illustrating a fabric drying step.

Figure 8a is a diagrammatic side elevation of a preferred method of applying, to one side of the cord fabric, the rubber compound, to produce the composite fabric of Figure 6, while Figure 8b is a similar view of an apparatus for applying the compound to the other face of the sheet, to produce the composite fabric of Figure 7.

Figure 9 is a diagrammatic plan view showing an elongated sheet of coated fabric, laid out and marked for subsequent cutting into blanks from which composite rolls are subsequently made;

Figure 10 is a perspective view showing a coated blank wrapped on a mandrel for the start of the rolling operation;

Figure 11 is a diagrammatic elevation showing a preferred manner of winding the blank of Figure 10 into the form of a roll;

Figure 12 is a fragmentary perspective view of the composite sheet of cord and unvulcanized rubber compound wound or rolled upon a wire or other core or mandrel, prior to partial vulcaniza tion;

Figure 13 is a fragmentary isometric sectional view showing a plurality of rolls, similar to the roll of Figure 12, in a mould during a preliminary,

partial vulcanizing step, subject to heat and pressure, where the rolls are compacted, densified and partially vulcanized; 1

Figure 14 is a fragmentary perspective view of the roll after the step of Figure 13 has been como pleted, showing how the narrow, laterally projecting fins may be trimmed off;

Figure 15 is a fragmentary, perspective view of the compacted, partially vulcanized composite roll after the narrow overflow fins have been trimmed ofl;

Figure 16 is a diagrammatic sectional view showing a buffing step, whereby'the partially vulcanized rubber on the surface of .the roll is removed;

Figure 1'7 is a fragmentary perspective view of the completed, semi-cured, compacted and bufled roll, from which a plurality of uniform plugs are cut;

Figure 18 is a side elevation of the roll with the wire or core removed, and indicating how the compacted roll is sliced or severed into a plurality of uniform sections or plugs of any desired thickness;

Figure 19 is a somewhat diagrammatic view. in vertical section illustrating the step of dipping the plugs in an unvulcanized rubber solution to coat all of the exposed surfaces thereof and to impregnate the cords on the circumferential surfaces of the plugs, which have been exposed by the buffing step;

Figure 20 is a perspective view of one of the plugs, after it has been coated with a tacky, unvulcanized rubber solution, for instance, by the dipping step of Figure 19;

Figure 21 is a vertical sectional view through I a final heel v'ulcanizing mould showing a manner of incorporating one of the plugs in a rubber heel blank:

Figure 22 is a vertical sectional view, similar to Figure 3, but showing a modification, and

Figure 23 is an enlarged diagrammatic view of the face of one of the improved plugs, showing the relationship between the cords and the partially vulcanized rubber compound.

Referring to the drawings, l indicates a rubber heel and 2 a rubber or composition half-sole in which the improved non-slipping wear plug 3 is irremovably amxed to become an inseparable part thereof in accordance with the invention.

In preparing the plug .for subsequent incorporation of the 'heel or sole blank, a specially made sheet of cord fabric 4 is used. This fabric I preferably consists substantially entirely of warp threads or cord 40 disposed in substantially parallel relation, with only sufiicienttransverse or weft threads therein to form a woven sheet which may be handled. The fabric preferred in actual practice is known as 13-3-3 carded American cord. Three No. 13 yarns are twisted to make one strand, and' three strands are twisted together to make each cord. There are approximately 23 cords per inch in the warp, while the weft threads are spaced substantially of an inch apart. The twist ply is 18.50-20.50, while the cable twist is 10-11. In other words, the three yarns are twisted between 18.50-20.50 times per inch of strand length. The strands in turn are twisted between ten and eleven times per inch to form the cable or cord. The weft threads are much thinner and have only sufficient strength to hold the warp cords in the desired relation during handling thereof. Preferably, they are weak enough to permitthe fabric to be readily torn on lines parallel with the warp cords. In the accompanying drawings, the thickness of the weft threads is somewhat exaggerated.

An elongated sheet of the cord fabric 4 is first run through a steam-heated drier of conventional design, represented diagrammatically in Figure 8, in order to drive out substantially all of the moisture normally present in the cords, so that they will be capable of absorbing a maximum amount of rubber compound in a subsequent operation, and so that there will be no moisture present in the composite roll when the latter is subjected to a partial vulcanizing operation under heat and pressure. 'Such moisture would be converted into steam in that operation and would cause the plug to blow or swell. The drying step performs the additional function of facilitating the union between the subsequently applied, compounded rubber since the rubber will not knit satisfactorily to cold fabric and it is important that the fabric is coated with the compounded rubber immediately after it is run through the drier and while it is still warm.

The dried, warm, elongated sheet of fabric is wound upon a roll 5 which is next positioned adjacent a calendering machine 1, comprising heated rolls la, 1b, 10, accurately spaced a predetermined distance apart. Rubber compound I is rolled into sheet form of accurately 'determined thickness through the bight between rolls la and lb. The fabric 4, unwound from the roll 5, passes under a tensioning and guiding bar I and is then drawn through the bight between the rolls lb and lc where the rubber compound 6 is applied thereto, and the fabric and rubber firmly united and compressed together to impregnatethe fabric sheet with the rubber compound. The composite sheet 8 leaves the roll 'lc, passes over a wrinkle-eliminating brush 1d and is wound into the form of a roll ill, with a liner sheet wound up therewith between the successive convolutions, to prevent the raw rubber compound from sticking to the uncoated face of the fabric.

then passes over three cooling rolls II, II, I2,

where the heat from the sheet is extracted. It is important to cool the rubber coated fabric, so

that it will not contain sufficient heat to prematurely vulcanize or scorch the rubber when it is subsequently wound into a. roll, which might readily occur if the heat applied to the rubber and the fabric by the calendering rolls remained therein. The sheet passes from the cooling rolls under a suitable tension bar where it is again wound up into the form of a roll It) with a liner 9a interposed between the convolutions, to prevent the unvulcanized, tacky, rubber compound coatings=from sticking to each other.

It is important that the thickness of the rubber sheets 6, So be carefully determined and controlled by the sheeting and calendaring rolls, so that the thickness of the final composite sheet will be a known constant.

Although it is preferred to apply a sheet of rubber composition to both faces of the cord fabric, satisfactory results have been accomplished by applying a rubber composition sheet to one face only. If desired, instead of applying the two sheets by separate calendering operations, both sheets may be applied simultaneously, by simply feeding two rubber composition sheets to the calender rolls with the cord fabric sheet between them.

Although the method of applying the rubber as described above is preferred, various other methods may be employed to form a unitary composite web. Such alternative methods may include what are known as (a) frictioning by means of calendering, (b) cementing by immersion or dipping or by spreading with suitable dough, (c) dip-coating and calendaring, (d) frictioning and coating, and (e) dipping and coating.-

The composite sheet 9 of cord fabric 6 and rubber composition 6, 6a in the roll I0, is next unwound and laid upon an elongated cutting table with the cord threads running longitudinally thereof (Fig. 9). The large sheet is then marked transversely by lines 3| into lengths suitable for the individual rolls subsequently to be made therefrom, e. g., 22 inches. After the elongated sheet has been so marked, an operator counts off, from one selvedge an-exact, predetermined number of cord strands, so thatthe plugs subsequently to be made may have an accurately determined number of strands therein, and so that the diameter and volume of the composite roll subsequently made may be accurately controlled. Since the number of cords in the fabric per inch of width may vary somewhat in different portions of the fabric, it is important to count the cords before the fabric is marked, in order that the number of cords in the blank may be determined with extreme accuracy. If the sheet were simply measured and then marked, a substantial variation in the number of cords might occur, depending upon the lateral tension on the sheet and other factors which might control the relative spacing of the cords or the number of cords per inch of fabric width. Of course, the number of cords varies with different sizes of plugs. In practice, the numbers range from 30-35 cords for a No. 5 size plug to 480-500 cords for a No. 16 plug, these size members being purely arbitrary commercial designations. of plugs are at present made commercially, and for each size a different number of cords is counted off and employed in the blank which is subsequently cut from the main composite web.

The counting operation may be quite readily performed, since the impressions of the cords in the fabric show through the surface of the rubber sheets calendered thereon. An operator carefully picks each warp thread with a pointed tool,

until the desired number of cords have been counted, whereupon a mark 30 is made which will indicate where the longitudinal cut, between two adjacent cords should be made, the line 3! for the transverse cuts having previously been marked on the sheet.

' After cutting the elongated web longitudinally and transversely into pieces of the desired size, each containing the desired number of cords and a predetermined amount of rubber compound, the sheets are wound upon a mandrel or core which may consist of a wire 35. This winding operation is performed under very substantial pressure and/or tension to produce a compacted composite roll, with a minimum of air spaces therein. One longitudinal edge of the blank cut from the elongated web is turned by hand upon the wire 35 (Fig. 10) and the winding is started by hand. Then, the wire is placed on a plane surface 36 under a substantially fiat rolling board 31. The board is moved forwardly substantially parallel to the rolling surface and rocked forwardly and downwardly to cause the composite sheet to be wound upon the wire. Suitable weight, in the neighborhood of between 175-200 pounds is applied to the rolling board 31 during the translational and rocking movements thereof, so that the convolutions of the roll are firmly pressed together as they are wound up, and air is substantially entirely excluded from between the layers. In practice, it has been found advantageous to have one man reciprocate the rolling board, while another stands upon the upper surface thereof to apply the necessary pressure the mould cavities are substantially equal to the size of the desired finished plug. It is important that the diameters of these cavities be slightly smaller than the diameter of the composite roll before vulcanization, to the end that the roll, during this partial vulcanization step, may be subjected to a high degree of radial compacting pressure, to substantially reduce the roll diameter and to form a densely compacted, unitary,

partially vulcanized structure wherein the cords are thoroughly impregnated by the rubber composition and all of the spaces between-the cords are filled with rubber compound and the laminations between the convolutions obliterated.

During the partial vulcanization in the mould. cavities l3, each roll is subjected to a temperature of approximately 296 F. for a period of substantially nine minutes, to produce the desired partial vulcanization. A pressure of approximately 442 pounds per square inch is actually applied to the rolls themselves, excluding the pressure taken up by the mould halves throughout the surfaces spaced from the cavities. This. pressure and heat causes a slight overflow of rubber composition from the mould cavities to the adjacent surfaces between the mould halves, with the result that fins 38 may be formed on the sides of the rolls which are subsequently trimmed off. I

As a result of this partial vulcanization under heat and high compacting pressure, the diameter of each roll is reduced from between of an inch to feof an inch, or more. For instance, the smallest'size commercial roll before vulcanization is %4, while, after compacting the partial vul-.

canization, it is a loss of about 9 of an inch. The importance of this compacting and partial vulcanization step, and the advantages resulting therefrom are discussed below.

After the rolls have been compacted and partially vulcanized, the fins 38, which have been squeezed laterally therefrom, are trimmed 01!, preferably by hand shears. It often happens that in addition to the rubber compound forced laterally from the mould cavities, a few cords will also be squeezed out and these are trimmed off with the fins. After this trimming operation, a cylindrical roll of uniform diameter is produced, having a continuous semi-vulcanized rubber layer on its .exterior surface, the rubber compound having been forced to the surface during the compacting and vulcanizing step.

The rolls so produced are next subjected to a 'buffing operation with a rapidly rotating wire brush 39, to remove this rubber layer from the outside of the rolls and to expose the cord surfaces. This bufling step is of importance, since it is desired to impregnate the cords on the surface of the roll with an unvulcanized rubber compound to effect an integral union of the plugs with the rubber heel blanks. Preferably, the bufllng is performed by'placing the surface of the roll in contact with the periphery of a rapidly rotating wire brush 33 and by manipulating the roll to subject all portions of its surface to the action of the brush.

After substantially all of the rubber on the exposed surface of the roll has been thus removed, the wire core or mandrel 35 is drawn therefrom, by pulling the roll longitudinally while the protruding' end of the wire is firmly held in a vice or the like.

The rolls are now ready to be cut or sliced into individual plugs of the desired thickness. Preferably, this operation is performed by an automatic machine which feeds the roll a predetermined,

adjustable distance between each slicing operation corresponding to the thickness or height desired in the finished plugs. Of course, any other suitable cutting mechanism may be employed.

The plugs 3 thus formed, having a central bore l therein, are next strung on wires 40, in accurately spaced relation; about twelve plugs to a wire. The wires and plugs are then dipped in a special liquid rubber compound 4|, containing unvulcanized rubber, solvents, curing agents, accelerators and the like, described below. Prefer- :ably, this compound is the same as the rubber compound originally applied to the cord fabric, with the addition of suitable solvents, such as benzol and hexane. Three dipping operations with intervening drying periods of about onehalf an hour are preferred, in order to provide an even, continuous coating of suitable thickness of unvulcanized rubber on all exposed surfaces of the plugs and to enable the compound to impregnate the cords on the circumferential surfaces of the plugs.

After the coated plugs have been dried for a suitableperiod-oftime, they are ready for assembly with unvulcanized heel blanks or biscuits in a heel vulcanizing mould by a final vulcanizing operation under heat and pressure. To this end, one of the prepared, coated, semi-cured plug sections is placed in each receiving aperture of a plurality of heel compartments lie of a vulcanizing mould IS, the latter being designed and con-,

structed for the manufacture of rubber heels in which the plugs 3 are embodied. The described mould is ordinarily adapted for the reception and curing of a plurality of heel blanks, and a central circular depression ll, of slightly greater diameter than the diameter of the plug, is provided in each heel compartment l5a. Such arrangement permits of a ready insertion of the prepared plugs 3 in the mould, and the raised wall He of each depression or cavity l'l aids in'maintaining the centered relation of the plug relative to the mould and heel during the vulcanizing operation.

A prepared heel blank or biscuit l8 of raw rubber-compounded with suitable curing agents,

such as sulphur and the like, and of substantially in which the plugs are confined. Moreover, the

partially vulcanized, densely compacted plugs resist distortion as the relatively soft, unvulcanized rubber is caused to flow around the plugs under the pressure in the mould, to embed the plugs in the heels. Hence, the individual threads or cords in the plugs retain their parallel relation,-

perpendicular to the tread surface, and are not displaced. The heels are then cured in the usual manner by the application of heat and pressure within the closed mould, as by means of a hydraulic press, for example, for twelve minutes, at 316 F., after which the sections of the mould are removed from the press, separated and the heels removed. During their confinement within the final mould, the heels and semi-cured plugs are completely cured by vulcanization and the vulcanizing agents of the heel combined with the rubber fabrication and curing agents embodied and included in each plug section, and also contained within the tacky solution with which the plugs are coated. This results in a permanent, integral, non-separable union between the plug sections and the rubber of the heel. Such vulcanized union renders each plug section an integral part of its respective heel, so that it cannot be subsequently displaced therefrom.

It will be understood that the mould surface lib of each blank receiving aperture I511 is provided with the desired embossed configuration to impart to the lower surface of the heel and plug any desired ornamental design.

It will be noted that the central apertures I3 01' each plug section 3 permits the reception therein of a portion of the rubber heel blank: as the same softens and flows under heat and pressure during the vulcanizing interval; The entrance of the rubber into the aperture is indicated at I! and augments the secure and vulcanized union at this point, thereby materially aiding in preventing any subsequent displacement of the plug relative to the heel or any tendency for its separation therefrom. Any portion of the aperture I! which does not receive outside rubber is closed and sealed by the application of the vulcanizing heat and pressure.

The upper section lid of thevulcanizing mould I6 is preferably provided with a depending portion 2|! disposed concentrically and in alignment with the plug sections 3. Such portion of the mould forms a depression or concavity II in the depressed portion 2| affords clearance for such relative upward and downward bodily movement of the plug and prevents the shock of impact being received directly by the wearer of the shoe. This movement of the plug is facilitated by the annular groove 25, formed in the face of the heel by the rib H in the mould. It will be understood that this vertical movement of the plug is not independent of the heel, as it is inseparably ,afilxed thereto. It is due to the resiliency of the rubber of the heel proper which alternately compresses and expands during use.

After. removal from the vulcanizing mould l6 and press, the heel sections are ready for trimming and use.

A thin piece or disc of binding or label stock indicated at 22 and which may be of substantially the same diameter as the plug, may be placed in the bottom of the circular depression I! prior to superposing the plug thereupon.

A second layer or disk of binding stock of similar configuration may be placed on top of the plug 3 before the mold is closed.

The described label stock is preferably composed of a compound having a stiffness or consistency intermediate that of the fabric composing the plug and the rubber of the heel. This affords a gradual merger from the stiff plug to the softer and relatively more resilient rubber heel compound, and facilitates the uniting or combining of these materials.

. This binding or label stock acts as a further binder between the heel and the plug during the curing or vulcanizing step and assists in completelycuring the plug and welding the plug and heel together to form a unitary article. The binding or label stock preferably consists of a compound of rubber together with the usual fillers and curing agents, which is milled on a Banbury or on a mill or both, prior to rolling into thin sheets and cutting out into the circular or other desired shape of the plug.

From the foregoing, it will be apparent that I have provided a frictional and non-slipping plug for rubber heels wherein the maximum resistance to wear is obtained by reason of the endwise engagement with the pavement or wear surface of each of the multiplicity of cord fabric strands of which the wear plug is composed. As compared to a fiat or sidewise engagement of a canvas or other fabric with the wear surface, such end engagement of the closely compacted rubberized fabric strands will afford a practically non-wearing and non-yielding surface as will be obvious. The provision of the hollow concavity 2| in the top or lift surface of the rubber heel adequately prevents the described resistance to wear being-imparted to the attaching surface of the shoe and to the wearer thereof. When in use the impact of the heel with the pavement or wear surface tends to move the friction wear plug upwardly coincidentally with the compression of the rubber of the heel. The difference in resiliency between the rubber heel proper and the wear plug is adequately compensated for by the aforesaid concavity or depression in the lift surface of the heel. which prevents the upper end of the plug or heel adjacent thereto fromrcontacting with the heel proper of the shoe. Since the wear plug is preferably positioned centrally of the heel and tothe rear thereof, where the impact with the pavement or other wear surface is normally received, the described invention provides a;

resilient heel in which the desired cushioned effect combined with maximum wear is afforded without running down of the side edges of the heel, since the wear plug receives the impact and prevents the same from being transferred to the relatively less resistant vulcanized rubber portions of the heel proper.

It is of paramount importance to maintain the individual cord strands in the plug in predetermined, substantially perpendicular relation to the tread surface of the heel, in order that the cords will wear evenly and will not become frayed. If the cords meet the tread surface of the heel on oblique lines, as when bias-cut fabric is used to make the plugs,'they will be likely to wear at an angle to the cord axes with the result that the ends of the cords, instead of wearing down smoothly, will unravel somewhat and present an unattractive, inemcient, fuzzy surface.

During the preliminary, partial vulcanization of the roll from which the plugs are ultimately cut, the roll is subjected to sufficient heat and sufficient compacting pressure to make the plugs subsequently cut from the roll, dense, unitary, nonlaminated, integral structures having sufllcient internal strength and resiliency to resist distortion, squashing or change in shape under the influence of forces applied to the plugs by the unvulcanized heel blanks and the mould sections during the final vulcanization of the heel blanks and plugs in the final moulds. When the final mould is closed under hydraulic pressure, the plugs are subjected to a high degree of axial, squashing pressure, imparted thereto by the blanks I8. If the plugs had not been compacted andpartially vulcanized they would have subfiows around and into intimate contact with plugs. Any slight distortion of the plugs under the initial mould closing pressure is then automatically corrected by the inherent elasticity or resiliencyof the plugs, which have been partially vulcanized. When the heel blanks l8 become soft and fluid, during the vulcanizing operation, the plugs return to their original shapes, if they have been previously slightly distorted, and in the finished product, the threads or cords are all substantially perpendicular to the tread surface.

, Hence, the compacting and partial vulcanization of the roll, prior to the incorporationof the plugs into the heel blank by a final vulcanizing action, is of importance'in producing the improved final product of the present invention, wherein the cords are all in parallel relation to each other and in perpendicular relation to the tread surface, and permanently bonded in the heel by vulcanization.

It is important that the compacting pressure applied to the composite rolls and the partial vulcanization in the mould halves I2, be so related to the pressure applied to the plugs and the heel blanks in the final, heel vulcanizing mould that the shapes of the plugs and the positions of the cords therein are not substantially changed during the later vulcanizing operation. These re-- quirements are satisfied if the pressure and temperatures indicated above are used in the partial vulcanizing step, for substantially the time specified, and more or less pressure may be applied in the final mould. In the usual practice, the heel blanks and plugs are assembled in the final moulds under pressures determined by the characteristics of the final product desired, as to composition, shape, surface configuration, resiliency, etc.

Many important advantages result from compacting, densifying and partially vulcanizing the elongated rolls in cylindrical moulds under heat and pressure, before the plugs are cut from the rolls, as compared with partially vulcanizing plugs cut from a roll consisting of fabric and unvulcanized rubber. The manufacturing operation is greatly simplified, since an elongated roll of uniform diameter may beconstructed to fit the cylindrical cavity in the mould, whereas, with the unvulcanized plugs, clifliculties are encountered in handling them, inserting them in the moulds and applying uniform compacting pressure to their circumferences. A roll constructed in accordance with the present invention is of uniform diameter from end to end prior to vulcanization. As a result, uniform compacting pressure is applied during the partial curing step. Therefore, a partially vulcanized roll of uniform diameter, density and volume, from end to end, is produced. Plugs cut from such a roll have identical characteristics, an essential factor in mass production of rubber heels.

As a result of the method of this invention, all of the rubber in the composite roll and in the finished plugs is uniformly partially vulcanized. The laminations between the various convolutions are entirely eliminated and all air pockets are eliminated. Moreover, as a result of the compacting pressure and partial, uniform vulcanization, there are no zones of weakness where the rubber is vulcanized less than at other zones. Hence, the fabric convolutions cannot be separated by the pressure applied to the plugs by the unvulcanized heel blanks in the final moulding operation.

The uniformity of partial vulcanization which results from vulcanizing the roll under heat and pressure in a cylindrical, preliminary vulcanizing mould, as stated above, eliminates the layers of rubber in the plugsand merges all of the rubber into an integral continuous mass. Each cord strand in the plugs is surrounded and encased by an enveloping body of uniformly partially vulcanized rubber which separates each cord from the others. This enveloping body of partially vulcanized rubber maintains the cords standing on end during the final vulcanizing operation with the result that the ends of the cords are exposed on the tread surface in the finished product.

In Figure 23 the relative positions of the cords and'the mass of partially vulcanized rubber are shown. As pointed out above, each cord 50 is composed of three highly twisted strands BI, 52 and 53. The rubber compound 55, it will be noted, not only envelops the individual cords 50 and fills the spaces therebetween, but impreg- -strands thereof, as well as the minute spacesnates the cords and fills the spaces between the between the yarns which make up each strand. Thus, each cord and each yarn and strand in each cord are held in place by the enveloping body of partially vulcanized rubber.

Any suitable rubber composition may be employed for coating the cord fabric 4, so long as it has the requisite plasticity and sheeting prop erties and so long as it will produce, in the partial vulcanizing operation, a densely compacted, uniform, non-laminated, tough structure. Preferably, a composition containing the following is employed:

Per cent Pale crepe rubber 72 Filler (clay) 14 Oxides 7.2 Ultra marine blue master batch less than 1 Accelerators .86 Stearic acid and rosin oil 3 Anti-oxidant Trace Sulphur 1.8

As stated above, liquid rubber composition which is used for coating the buffed and cut plugs may consist of the foregoing compound with suitable solvents. For instance, 50 pounds of the material, compoundedas above, may be dissolved in a mixture of 15 gallons of benzol and 35 gallons of hexane.

It must be understood that the invention is not limited to these specific compositions, but includes all materials adapted to function in a similar manner.

The composition of the rubber heel blanks or biscuits may be varied between the wide limits and any suitable composition known to the prior art may be employed.

The invention is not confined to the manufacture of anti-slipping plugs of any particular size range for rubber heels and soles and the dimensions given in this specification are illustrative of only, covering the sizes used commercially at the present time. Obviously, the sizes of the plugs may be decreased or increased to any extent desired, depending upon the use to which they are to be put, by simply winding up and partially vulcanizing rolls of the desired diameter and'cutting plugs therefrom, of any desired thickness.

The modification shownv in Figure 22 illustrates a preferred combination of plug and sole or tap, as distinguished from a heel. The tap sole 2 is relatively thin and for this reason it is not practical to provide, above the plug 3, a cavity or depression 2|, such as is shown in Figure 3, in connection with a rubber heel. To compensate for the absence of such a depression, and to 'aiford the desired resiliency of movement of the plug relative to the sole when in use, a section or area 24 of more resilient rubber, properly compounded, is inserted in the sole blank, coextensive with and immediately above the plug 3, to give the desired cushion effect to the plug at this point in use. Such compounded more resilient rubber 24 also acts to increase and render more efi'ective the binding union between the plug 3 and. the rubber of the sole proper.

This application is a continuation-in-part of my prior application Serial No. 721,028, filed April 17, 1934. i I

I claim:

1. The process of manufactur g rubber heels which consists of uniting a shee of fabric and a sheet of rubber to form a composite sheet, said rubber having curing agents therein, winding said composite sheet onto a mandrel to form a roll, partially curing said roll to vulcanize the adjacent convolutions of rubber and fabric together, cutting said partially cured roll into sections, dipping said sectionsin a tacky rubber solution having curing agents therein to form wear plugs, and vulcanizing said plugs in the tread portion of a rubber heel to inseparably unite the plugs with said heel, the strands of fabric included in said wear plugs being disposed substantially perpendicular to the said tread portion of the rubber heel.

2. The process of manufacturing anti-slipping wear plugs for rubber heels and soles, which consists in uniting a sheet of fabric and a sheet of rubber to form a composite sheet, said rubber having curing agents therein, winding said composite sheet onto a mandrel to form a roll, partially curing said roll to vulcanize the adjacent convolutions of rubber and fabric together, cutting said partially cured roll into sections, and dipping said sections in a tacky rubber solution having curing agents therein to form wear plugs.

3. A substantially solid wear plug for a rubber heel or sole, consisting of a tightly rolled composite sheet of fabric and rubber, the strands of a said fabric in each convolution ofthe roll being vulcanized to the adjacent convolutions of rubber, the outer surfaces of said wear plug being impregnated with a tacky rubber solutionhaving curing agents therein to permit said wear plug to be permanently and securely united by heat vulcanization to the adjacent rubber material of said heel or sole.

4. A substantially solid wear plug for a rubber heel or sole, consisting of a tightly rolled composite sheet of cord fabric and raw rubber, the strands of said fabric in each convolution of the roll being vulcanized to the adjacent convolutions of raw rubber and arranged perpendicu larly to the end surface to provide a maximum of resistance to wear, the outer surfaces of said wear plug being impregnated with a tacky rubber solution having curing agents therein to permit said wear plug to be permanently and securely united by heat vulcanization to the adjacent rubber material of said heel or sole.

5. In the manufacture of rubber heel plugs, the method which comprises providing cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating the elongated sheet with an unvulcanized rubber compound, winding the sheet into a roll about an axis substantially parallel to the cords, subjecting the composite roll to radial compacting pressure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber compound therein to form an integral, densely compacted, unitary structure, whereby there may be cut therefrom heel plugs having sufficient internal strength to resist distortion and movement of the cords during subsequent assembly by vulcanization under heat and pressure into heel blanks, and cutting the roll transversely to form such heel plugs.

6. In the manufacture of rubber heels having plugs therein, the method which comprises providing cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating the elongated sheet with an unvulcanized rubber compound, winding the sheet into a roll about an axis substantially parallel to the cords, subjecting the composite the elongated sheet with an unvulcanized rubber.

roll to radial compacting pressure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber. compound therein to form an integral, densely compacted, unitary structure; whereby there may be cut therefrom heel plugs having sufficient internal strength to resist distortion and movement of the cords during subsequent assembly by vulcanization under heat and pressure into heel blanks, cutting the roll transversely to form such heel plugs, and assembling the plugs with unvulcanized rubber heel blanks with-the cords of the plugs extending perpendicular to the wear surface of the heels, and under heat and pressure vulcanizing the blanks and completing the vulcanization of the plugs.

7. In the manufacture of rubber heels having plugs therein, the method which comprises providing cord fabric sheet with the cords therein disposed longitudinally of the sheet inparallel relation, coating the elongated sheet with an unvulcanized rubber compound, winding the sheet into a roll about an axis substantiall paral-' the plugs with unvulcanized rubber heel blanks with the cords of the plugs extending perpendicular to the wear surface of the heels, and

under heat and pressure vulcanizing the blanks,

and completing the vulcanization of the plugs.

8. In the manufacture of rubber heel plugs,the method which comprises providing. a cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating the elongated sheet with an unvulcanized rubber compound, winding the sheet into a roll about an axis substantially parallel to the cords, subjecting the composite roll to radial compacting pres sure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber compound therein to form an integral, densely compacted, unitary structure, whereby there may be cut therefrom heel plugs having sulficientintemal strength toresist distortion and movement of the-cords during subsequent assembly by vulcanization under heat and pressure into heel blanks, removing from the exterior surface of the partially vulcanized roll the surface layer or rubber, thereby exposing the cords on the surface, and cutting the roll transversely to form such heel plugs.

- 9. In the manufacture of rubber heel plugs, the method which comprises providing a cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating compound, winding the sheet into a roll about an axis substantially parallel to the cords, subjectlng the composite roll to radial compacting pressure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber compound therein to form an integral, densely compacted, unitary structure, whereby there may be cut therefrom heel plugs having sufficient inthe plugs with an unvulcanized rubber compound.

10. In the manufacturing of rubber heels having plugs therein, the method which comprises providing a cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating the elongated sheet with an unvulcanized rubber compound, winding the sheet into a roll about an axis substantially parallel to the cords, subjecting the composite roll to radial compacting pressure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber compound therein to form an integral, densely compacted, unitary structure, whereby there may be cut therefrom heel plugs having sufficient internal strength to resist distortion and movement of the cords during subsequent assembly by vulcanization under heat and pressure into heel blanks, removing from the exterior surface of the partially vulcanized roll the surface layer of rubber, thereby exposing the cords on the surface, cutting the roll transversely to form such heel plugs, coating the exterior surfaces of the plugs with an unvulcanized rubber compound, and assembling the plugs with unvulcanized rubber heel blanks with the cords of the plugs extending perpendicular to the wear surgated cord fabric sheet with the cords therein disposed longitudinally of the sheet in parallel relation, coating the elongated sheet with an unvulcanized rubber compound, counting a predetermlned number of cords in the sheet and cutting blanks therefrom containing the counted cords, winding each blank into a roll about an axis substantially parallel to the cords, subjecting the composite roll to radial compacting pressure, and, while the roll is held compacted, partially but incompletely vulcanizing the rubber compound therein to form an integral, densely compacted, unitary structure, whereby there may be cut therefrom heel plugs having sumcient internal strength to resist distortion and movement of the cords during subsequent assembly by vulcanization under heat and pressure into heel blanks, and cutting the roll transversely to form such heel plugs.

12. A plug for rubber heels or soles, comprising a vulcanized integral body of convolutions of rubber and cord fabric having the cords disposed perpendicularly to the wear surface of the plug, at least one face of the plug being substantially free of rubber at the ends of the cords, the conand having thecords disposed parallel to the axis of the roll, the convolutions being inseparably united into a densely compacted unitary structure, the exterior surface of the roll having the surface layer of rubber removed therefrom,

thereby exposing the cords on the surface.

ALBERT A. ESTERSON. 

